In order to obtain further insights into the mode of protection afforded by conversion coatings on aluminium substrates, Scanning and Transmission Electron microscopy techniques and potential measurements was employed to monitor variously treated aluminium specimens in chloride environments. Examinations revealed that conversion coated aluminium with top lacquer coatings and subsequently subjected to Chloride environments prevented pitting of the substrate. However, pits were observed on ‘bare’ aluminium and those with top lacquer coatings after being exposed to similar environments. The ‘bare’ chromate coated specimen revealed pits plugged by corrosion products suspected to be hydrated Cr III oxide and/or hydroxide formed through the reduction of Cr VI species present in the coating. Such a capability was not observed for the ‘bare’ chromate-phosphate specimen.
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